Epilepsy affects 1% of the world's population. Epileptic seizures can be debilitating because of the associated involuntary motor phenomena and impairment of consciousness. Uncontrolled seizures can lead to poor quality of life, inability to maintain gainful employment, inability to drive, and premature death. About one-third of epilepsy subjects do not respond to medication treatment, and require surgical resection or neurostimulation to control their seizures. Surgical treatment tends to be successful in only one-half to two-thirds of subjects, depending on the specific brain region targeted. Intracranial recordings of a subject's seizures are often necessary to accurately localize the seizure focus prior to surgical resection or placement of implantable neurostimulator leads. Such intracranial recordings of a subject's seizures require a surgical procedure to place the electrodes on the brain surface or within the brain, followed by continuous video-electroencephalographic (EEG) monitoring for several days coupled with withdrawal of the antiseizure medications to induce seizures. This procedure typically involves several days of hospitalization and carries a significant risk of morbidity, including hemorrhage and infection.
For presurgical localization of the seizure focus in subjects with epilepsy, the seizure onset zone (SOZ) is commonly used as an indirect measure of the theoretical epileptogenic zone (EZ), although the correlation between the two may not always be accurate. Although evidence suggests that the SOZ defined by the electrode channels or contacts showing ictal high-frequency oscillations (HFOs) or infraslow activity may be superior to that defined by the conventional frequency activity (CFA), it does not obviate the need for obtaining ictal recordings.